The present invention relates to a supply device for supplying rubber material to a cutting device, which supply device towards the cutting device is provided with:
an unwinding trestle holding a stock of rubber material,
a supplying table having a supplying mechanism for supplying the rubber material to the cutting device and
a space between the unwinding trestle and the supplying table, which space is suitable for taking up a loop of rubber material forming a stock buffer.
Such a supply device has been used for years. The supplying table is placed in front of the cutting device, and behind the cutting device a discharge system is placed, usually a conveyor belt, for discharging cut strips of rubber material. In front of the supplying table an unwinding trestle with a stock of ruber material is placed, in which between the unwinding trtestle and the supplying table a loop of rubber material is present. The operation of the assembly of such a supply device, cutting device and discharge system is intermittent. First rubber material is supplied, subsequently it is cut and then it is discharged. Depending on the exact design of the assembly these steps may partially overlap each other. During the operation of the whole, the loop works like a stock butter of rubber material to be supplied, ad the length of the loop is kept reasonably constant. In practice, however, it has appeared that the width of cut strips of rubber material is not the same everywhere. In the case the rubber material has been reinforced with cords of steel, textile or aramide, it has also appeared that at the beginning and at the end of the cut the cords are not always equally long. This leads to rubber strips of inferior or insufficient quality.
It is an object of the present invention to provide a supply device for the supplying of rubber material to a cutting device as a result of which the accuracy of the cut strips of rubber material is improved.
To that end a supply device of the kind described above is characterized in that between the space for taking up the loop of rubber material and the supplying table a first conveyor having a drive is placed.
The invention is based on the insight that the inaccuracy in the width of the cut strips of rubber material is caused by the weight of the rubber material present in the loop. Because of this weight the rubber material present on the supplying table can be retracted, as a result of which the position of the rubber material with respect to the cutting device is not accurately defined. Moreover, during the steps to be carried out of supplying, cutting and discharging, the length of loop is not always constant, as a result of which the weight of the loop differs. By, according to the invention, using a first conveyor between the loop and the supplying table, said first conveyor functions for buffering the weight of the loop of rubber material. As a result a more controlled supply to the supplying table is possible as well.
Moreover the use of the device according to the invention gives a solution to the following problem. Usually the rubber material and the cords present in it, are cut into strips by the cutting device at an angle of for instance 22xc2x0 (other values are possible as well). After the cutting device there usually is a splicer in which the so-called trailing end of a strip is attached, spliced, to the so called leading end of another strip. The splice is accurate when at the location of the splice there is no difference in cord length, in other words when the strips are equally wide everywhere and have the exact same angle. Small differences in width and in the cutting angle, for instance a difference of xc2xc mm in width or xc2xcxc2x0 in the angle, which differences are hardly measurable and which in the known device are caused by tensile force on the rubber material as a result of the weight in the stock buffer loop, in a strip having for instance a width of 200 mm and a cutting angle of 22xc2x0, respectively, result in a measurable difference in cord length of 0.67 mm and 5.8 mm, respectively. Because of the supply device according to the present invention tensile force on the rubber material is prevented, and as a result no deviations in the strips arise. The final result is that the strips can be spliced to each other very accurately, in which no or in any case less differences in cord length arise that may cause the arising of deviations known in the art as xe2x80x9cdogearsxe2x80x9d.
Thus the supply device according to the present invention ensures that the rubber material is always placed in a defined manner with respect to the cutting device, and that the rubber strip to be manufactured in the end are equally wide everywhere, and that the cords present in the rubber material are equally long at the beginning and the end of the cut.
Preferably the first conveyor is placed at a distance above the supplying table. As a result rubber material arrives on the supplying table from above. This results in a certain bending in the rubber material where it arrives on the supplying table, which bending is defined by the rigidity of the rubber material. Said bending ensures a pushing or urging force, as a result of which the material further on at the supplying table remains in contact with the cutting device.
In a supply device described above preferably a second conveyor having a drive is placed between the unwinding trestle and the space for taking up the loop of rubber material. In this way deformation near the roll is also prevented. Additionally the length of the loop can be checked better, and the weight can be compensated better. It is preferred here that the second conveyor is placed at a distance above the unwinding trestle. First of all the weight of the loop is optimally compensated in this way. Additionally, by placing the second conveyor higher the space for the loop, which in actual practice will have a total length of 2.5 m, can be realised more easily.
Preferably the first conveyor is provided with means for centring the rubber material. It is preferred that the first conveyor is provided with means for positioning a side of the rubber material. It is preferred here that the first conveyor is provided with sensors for detecting the position of the rubber material and with an actuator for positioning the rubber material. In this way the accuracy of the supplying can be improved further.
Preferably the supplying mechanism of the supplying table and the drive of the first conveyor operate synchronously during a supplying movement of rubber material in the direction of the cutting device. It is preferred here that a sensor is provided for measuring the location where the rubber material arrives on the supplying table, which sensor issues a control signal to the supplying mechanism of the supplying table and/or the drive of the first conveyor.
Preferably a revolving roller is placed above the supplying table near the location where the rubber material arrives on the supplying table.
Preferably, when a first and second conveyor are provided, a bridging flap that can be swung aside is provided between the second and first conveyor.
Preferably, when a first and second conveyor are provided, means for centring rubber material are placed between the unwinding trestle and the second conveyor. Means for positioning a side of the rubber material preferably are placed between the unwinding trestle and the second conveyor.
Preferably, in a supply device according to the invention means for centring rubber material are placed between the supplying table and the first conveyor.
Preferably, in a supply device according to the invention means for positioning a side of the rubber material are placed between the supplying table and the first conveyor.
In a supply device according to the invention the supplying table preferably has a number of parallel conveyor belts, driven by one central drive.
Preferably the parallel conveyor belts are slidable here with respect to each other in longitudinal direction.
It is preferred, in supply device according to the invention, that the supplying table is provided with means for generating a vacuum and/or a magnetic field.
In a supply device according to invention the first conveyor preferably is provided with first means for an almost slip-free retaining and transport of the strip on the first conveyor. The first conveyor can be provided with first means for retaining the strip on the transport surface of the first conveyor. Preferably the first means are provided with second means for generating a vacuum and/or a magnetic field on the transport surface.